Zeolitic materials, both natural and synthetic, have been demonstrated in the past to be useful as sorbent materials and to have catalytic properties for various types of hydrocarbon conversion reactions. Certain zeolitic materials are ordered, porous crystalline metallosilicates having a definite crystalline structure as determined by X-ray diffraction (XRD). Within the zeolitic material there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Because the dimensions of these pores are such as to accept for sorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as “molecular sieves” and are utilized in a variety of industrial processes.
One type of zeolite structure used for catalytic processing of petroleum streams is ZSM-48, a disordered high-silica zeolite with a one-dimensional 10-ring pore system. U.S. Pat. No. 4,397,827 discloses ZSM-48 and its preparation using a mixture of a C2-C12 alkylamine and a tetramethylammonium compound. The framework structure of ZSM-48 has been assigned the three-letter code *MRE by the Structure Commission of the International Zeolite
According to R. F. Lobo et al. (J. Am. Chem. Soc. 2002, 124, 13222-13230), ZSM-48 is not a code for one material but for a family of materials with different degrees of disorder. T. Wilhammar et al. (Z. Krystallogr. 2013, 228, 11-27) report that other materials of *MRE framework type include COK-8 (described in Chem. Mater. 2009, 21, 371-380), EU-2 (described in U.S. Pat. No. 5,098,685), EU-11 (described in J. Catal. 1984, 85, 135-142), IZM-1 (described in U.S. Pat. No. 7,771,703), and ZBM-30 (described in European Patent Application No. 0046504). U.S. Pat. No. 9,802,830 discloses molecular sieve SSZ-91, a molecular sieve belonging to the ZSM-48 family of zeolites.
A number of organic compounds have been shown to direct the synthesis of *MRE framework type molecular sieves including organic linear amine and polyamine compounds, diquaternary alkyl ammonium compounds and glycols.
U.S. Pat. Nos. 5,075,269 and 7,482,300 disclose the synthesis of ZSM-48 using conventional sources of silica and alumina in the presence of a hexamethonium salt directing agent. ZSM-48 prepared according to U.S. Pat. No. 5,075,269 is reported to have a SiO2/Al2O3 molar ratio of at least 100. The synthesis Example produced a zeolite having a SiO2/Al2O3 molar ratio of 170. ZSM-48 prepared according to U.S. Pat. No. 7,482,300 is said to have a SiO2/Al2O3 molar ratio of less than 110, but the lowest SiO2/Al2O3 molar ratio reported in the Examples is ˜80.
Zeolites are kinetically (but not thermodynamically) stable towards conversion to denser framework structures (e.g., α-quartz). As a result, their synthesis often involves the formation of structures of intermediate stability in the course of forming the ultimate target structures, which are often rendered stable only by the use of specific organic or inorganic cations. Recently, transformations of one zeolite structure into another one—interzeolite transformations—have been explored because they can provide a strategy for the selective synthesis of specific structures, often with shorter synthesis times. The mechanistic details of such interzeolite transformations, however, remain unclear and predictions of their success largely empirical.
According to the present disclosure, it has now been found that interzeolite conversion of an aluminosilicate zeolite of FAU framework type in the presence of hexamethonium cations is effective in the production of *MRE framework type molecular sieves at higher aluminum concentrations than those previously exemplified.